In view of the enhanced antigen neutralizing capability imparted by the catalytic function, the investigator and his colleagues propose to develop catalytic antibodies (Abs) capable of cleaving the epidermal growth factor receptor (EGFR) for immunotherapy of cancer. This goal has become feasible because of the acquisition of the following basic science knowledge: a subset of Abs express peptidase activity; the activity is encoded by a germline gene for the variable(V) region of the light chain subunit; the catalytic site is structurally similar to serine protease sites found in non-Ab enzymes; and the synthesis of antigen-specific catalytic Abs is increased in autoimmune disease. In aim 1, the EGFR binding VH domains cloned by phage display from a mouse immunized with EGFR-expressing cells will be conjugated to an available catalytic VL domain to generate EGFR cleaving Fv constructs. In aim 2, catalytically proficient EGFR-cleaving Fv domains from autoimmune diseased mice immunized with EGFR will be isolated from a phage displayed library. Fv species that express the germline encoded catalytic activity and the somatically acquired specificity for EGFR will be selected. In aim 3, they will attempt to force the immune system to use the germline encoded catalytic site for the synthesis of the Abs to EGFR. To this end, a novel phosphonate ester transition state analog of an EGFR peptide will be prepared and employed as the immunogen. In aim 4, the ability of the catalysts to reverse the tumorigenicity of the EGFR-expressing human cell line will be studied by measuring the inhibition of EGFR auto-phosphorylation, inhibition of cell proliferation in culture, and inhibition of the growth of established tumors in athymic mice. The investigators expect the proposed studies to generate catalytic Fv constructs capable of permanent and efficient inactivation of EGFR, and to establish the validity of using catalytic Abs for tumor immunotherapy.